10 replies to this topic

Hi all,
I have a situation.I need to transfer liquid from one tank to another.The liquids are transfered in batches and all batches are different.Because of space constrain I have to use only a single pipeline.But dude to pipe left over there is cross contamination which i do not desire.I believe their is left over because the pipeline has a horizontal section without any inclination.So i plan to give inclination to this horizontal section.The liquid is transfered using compressed air.

Can some one tell me is there any better way to transfer which can ensure no left over in the pipe line(any pump or any thing else)
Is providing slope solve my purpoe??

[sgkim]

If the liquids are not flammable, vacuum transfer can be one of the options. -sgkim

[Art Montemayor]

gatty:

This is a very practical problem and one that directly impacts on final cash product quality – a factor that directly affects company cash flow. As such, it should be of importance to every engineer facing similar situations.

I’ve had a lot of experience with this subject and have dealt successfully with such applications as:

• multiple batch reactors producing multiple, varied products – all of them classified as low sales volume, high profit mark-up;
• multiple storage tanks used for variable, high mark-up chemical products; and,
• critical transfer of hazardous liquid chemicals from railcars or storage tanks to other storage tanks.

Some of these situations have required careful and meticulous scheduling of production sequencing. Sometimes you can tolerate some level of contamination (within the product specs) and you therefore schedule your production runs so that similar products follow each other within the same piping system. However, the “bottom line” (net result) is that there is inevitable contamination taking place. In other words, some residual product is always left behind, within the interconnecting piping and fittings, and it is practically impossible to avoid this situation regardless of whether you use a pump, a pneumatic system (an “acid egg” type of system), or a vacuum.

When you resort to employing a piping system (with all its inherent design factors – such as fittings, valves, low points, off-sets, elevation differences, etc., etc.) you will always have residual fluid left over within the system. There is no way you or anyone else can avoid this eventuality. All that is left for a concerned engineer to do is to:

1. Design the original system with all the important criteria required to minimize the residual effect – never quite eliminating it; and/or,

2. Employ post-transfer techniques that will dispose of the majority of the residual, undesirable liquid.

Ingenuity (the real part of engineering) is employed in both cases to resolve the problem. There are instances where one product is so expensive to produce and carries such a very high price that either a thorough line wash-out and post solvent flushing + extensive rinsing and drying is called for OR an independent piping system is used exclusively for this line of product. I will only discuss variable products in common piping systems for now.

The first step, initial process design, should incorporate positive-sloped pipe in the proper direction and with positive draining and disposal accommodations. Piping break-outs, traps, flanged connections, flush-out and spray injections are just some of the methods incorporated.

The second step opens up the prospects of using your ingenuity and common horse sense. You can use internal solvent spraying, flushes, draining, positive pump-arounds of flushing liquid, and subsequent purging and drying out methods with hot, inert gas (Nitrogen). The most effective and positive method I’ve come across and used effectively is “Pigging” the transfer lines. This method has assured the quickest, safest, and most positive method of ensuring proper, high-quality product transfer for the next, subsequent liquid using the same line. However, note that careful and experienced design engineering is required of the involved piping system in order to incorporate a safe and effective pigging operation. In other words, you just can’t walk out into the plant at any given time and impose a process transfer line to pigging unless it has been properly designed for the purpose. As usual, this means that the operation must have been carefully and logically planned out PRIOR to installing the piping transfer system – a characteristic that is not usually common place in today’s management-run process industry. In my experience it is more than probable that managers, planners, design engineers, and other management individuals never consider that there will be cross-contamination problems when “saving capital investment” by imposing a common piping transfer system for all products. This is a common failing of today’s inexperienced and profit-oriented engineers and managers. Therefore, when the problem raises its ugly head at the plant level, the plant engineer(s) are left alone to resolve a critical cash flow problem. I know all too well what will happen when a customer receives a tanker shipment of product that is off-spec: he’ll immediately reject it and file a serious and threatening letter to your company advising of all the costs and losses that his company is incurring due to your contaminated product. This is why I’m going to lengths to write this response.

A different situation occurs when you use a pneumatic method to transfer a liquid product – as opposed to using a pumped system. The difference is the safety hazards involved with the pneumatic system. This is the subject of yet another and totally dedicated thread in the future and I won’t comment on it here for it will take a lot of space to address it in the manner it deserves. I hope some interested young engineer writes a question involving this critical subject. I’ve gone through a lot of grief and experience in that subject and look forward to sharing my key learnings with others.

And by the way gatty, please employ the proper spacing between your sentences when you write your posts or replies as well as proper capitalization of the personal pronoun "I". It is next to impossible to try to follow your communications when you run your sentences one after the other without the proper TWO SPACES to separate each sentence. This has nothing to do with the language or with the grammar. It has a lot to do with common courtesy in order to facilitate the reader the opportunity to clearly read and interpret what it is that you are writing. This is common, proper communications and is the tool that leads to proper understanding of the content and therefore leads to a proper and correct response.

I hope this experience is of some help to you.

[ranjith kumar]

Hi all,
I have a situation.I need to transfer liquid from one tank to another.The liquids are transfered in batches and all batches are different.Because of space constrain I have to use only a single pipeline.But dude to pipe left over there is cross contamination which i do not desire.I believe their is left over because the pipeline has a horizontal section without any inclination.So i plan to give inclination to this horizontal section.The liquid is transfered using compressed air.

Can some one tell me is there any better way to transfer which can ensure no left over in the pipe line(any pump or any thing else)
Is providing slope solve my purpoe??

It seems it is better to apply pressure and de pressure method or pass the solvent thru the lines in which it dissolves after that flush the lines with the solvent which you have to use in next batch.

Thank you so much ART for your reply. I will definitely keep in mind your suggestions about the discussion and also my wrighting style.
I would be greatful if you could give me a bit more insight on "Pigging" and also about the transfer method.

In the present scenario at this plant we use acid-egg type arrangement to transfer.Do you suggest that we should do away with it for safety hazards. I would be greatful if you could give me a bit more details about the safety hazard issues and tell me some alternative ways to transfer the liquid.

Finally I would like to ask you that if i go ahead and provide a positive slope to the line,how do I decide on the slope.

I would be greatful to receive your reply,


Thanks and regards,
Gautam

[Art Montemayor]

Gautam:

I will be very pleased to respond to your specific questions and needs. It is a pleasure to respond to engineers who show interest in learning from other's mistakes and experiences. It it is a mark of practical intelligence which should be a standard with all engineers.

At the moment I'm tied up with a very high priority project and it will take a couple of days to compile a complete and detailed answer to your specific questions as well as furnish you with references and equipment details. I will try to put together an Excel Spreadsheet with illustrations on some of the details. Bear with me and I will furnish you with the specific answers to your questions and needs.

Suffice it to say that I understand perfectly well how uncomfortable you must feel with an "acid egg" type of liquid transfer - especially if it is done on a hazardous fluid and into a very low pressure tank (such as a storage tank). I've been there and the feeling isn't very comforting.

I'll do my best in trying to help out.

[djack77494]

Gautam:
I'm sure you'll get a complete and high quality explanation from Art. In his absence, I'll offer a few comments.

The sloping of transfer lines to the receiving vessel, of course, makes good sense. No extreme measures are needed here - you're basically interested in ensuring that there are not low spots where liquid can be retained. I would suggest a slope of say 1:12 to 1:15 as being more than adequate for this purpose. Complete the implementation of this concept by ensuring that there are no other spots where liquid can be trapped, such as low point drains. Though this may seem obvious to you, it may not be so to those who follow you in implementing your concepts. Don't let your careful planning be easily defeated.

The term "pigging" refers to the use of a mechanical device which passes through your pipeline to displace any liquid or other materials that might otherwise be retained in the piping. The pig is designed so that it occupies the majority of the pipe's cross sectional area. It effectively acts as a ram to push the liquid (and solids) in the pipe forward and out. A motive fluid, such as air, water or process fluid, is typically used to drive the pig through the piping. When employing a pigging system, the piping must be designed with this in mind. Bends, constrictions, restrictions, etc. must be either avoided or somehow designed around (best if avoided). I have used pigs mainly in cleaning service where they remove excessive quantities of solids and "muck" that would otherwise build up in crude oil production lines. It is not necessary for these pigs to scour the lines to the point of leaving no liquids behind. Your case may be different if you are using high value raw materials that could be contaminated with alternate materials. However, I'm sure there are pigs designed for that purpose. If you go this route, you will need a pig launching station where the pig is introduced into the piping system, and a pig receiving station.

Good luck in your pursuits,
Doug

Thank you so much for your reply ART and DOUG .

I will be eagerly waiting for further inputs from your side.
Another issue is that I need to design a mixing cylinder along with impeller design within a week.Issue is that i am an undergraduate chemical engineer and do not have much idea about how to design that.I have access to the only two books:McCabe Smith and Perry.But am not getting a very good idea how to go about it .I will be really obliged if you can send me some online document or suggest some way to design it .



Thanks and regards,
Gautam

[Art Montemayor]

Gautman:

Please tell us if this is an industrial application you are involved in or an academic problem. This is the Industrial Professionals Forum and I've assumed you are facing a real-world problem. Is this correct or wrong?

We need to know in order to schedule our time and priorities. If you are facing an industrial safety situation, that is one thing. However, if the question arises from an academic interest or is a homework problem, that is another issue.

Please respond. We want to help; but you must be honest with us.

Dear ART,
This is a real situation and although i am jus an undergraduate ,i have been given this project as a part of my internship in order to gain industrial exposure .This is very essential for me as my future with this company is based on my this performance.Hence i would appreciate any kind of help from your side as being an undergraduate its very essential for me to seek the kind of experience you have.Eagerly awaiting a reply.

Thanks and regards,
Gautam

[Art Montemayor]

Gautman:

To obtain some valuable information on the technique and art of employing a pigging operation on process pipe lines, go to:

http://www.pigsunlim...gingformula.asp

http://www.pipepigs.com/

http://www.hps-pigging.com/demo.html#

I would emphasize the pigsunlimited site as one suited to your application. You should easily find enough basic and detailed information on the pigging technique within the Internet and this should eliminate any need for me to go into any details on that subject here. I not only believe that this knowledge is critical for your application, I also believe it should be the answer to your concerns and product quality problems now and in the future. Bear in mind that the correct application of pigging requires a lot of piping and fluid transfer common sense and practical engineering. This is not nuclear science, but it requires careful and detailed study in allowing for the practical needs and characteristics of your application. If presented and applied correctly, I have no doubt that your employers will be very pleased with the results of such an application.

Pay particular attention to the instructions and guidelines of the pig manufacturers and their specifications for the application of their pigs. All piping should be as short and simple as possible. Very long radius elbows or bends should be employed as well as a minimum of line fittings. You may easily be forced to replace the existing piping in order to ensure a successful retrofitting of a pigging installation.

For the employment of pneumatic liquid transfer (“acid egg technique”), I would strongly urge you to contact Endress + Hauser, the German instrument manufacturer who specializes in producing some very accurate flow detection switches. Their website is:

http://www.endress.com/

I have applied their switches in successful pneumatic transfer of such troublesome and hazardous applications as the railcar unloading of hot, liquid Phenol into Low Pressure storage tanks. This application is a very hazardous and nasty job due to the following characteristics:

1) Phenol is a solid at ambient temperatures and has to be maintained heated (as well as its entire path) at approximately 120-125 ^oF in order to ensure it is a liquid. This necessity is vital because any solidification of Phenol immediately imposes a severe pressure drop or total pluggage of the system. To effect this, the entire system must be heated and/or traced and the piping must be straight, sloped and self-draining.

2) A supply of 100 psig Nitrogen gas is employed to furnish the pneumatic power to transfer the liquid from a railcar into an atmospheric storage tank. A dip pipe is used to evacuate the liquid from the railcar and a dip pipe is used to inject the liquid into the storage tank.

3) Once the liquid reaches the entrance of the dip pipe in the railcar, 100 psig Nitrogen being supplied to the railcar vapor space will immediately enter the transfer line and continue on towards the storage tank. This 100 psig supply of Nitrogen presents a grave danger to the storage tank because the storage tank is capable of withstanding only 1.5 psig as a MAWP.

4) If the 100 psig Nitrogen is allowed to reach the atmospheric tank, not only will a dangerous over-pressure scenario occur, but excessive turbulence and toxic emissions will occur from the tank.

The insertion of an Endress + Hauser flow switch in the flow line at the tank car outlet enabled us to immediately activate a block shut-off valve at the storage tank inlet. The flow switch detected the difference between the liquid and the gas flow and, thereby, was able to detect when the high-pressure Nitrogen broke through into the flow line. In this manner, we were able to mitigate a dangerous situation and avoid emissions. I forget the exact description and model of the switch, but an Endress + Hauser representative should be readily prepared to help you out on this application if you are interested. E+H was very helpful and cooperative in helping me resolve this situation. I firmly believe that all pneumatic liquid transfer operations should be protected by such a system or something similar. To rely on human reactions to shut off the flow before the gas enters the target tank is not a reasonable basis of design.

I hope this information is of benefit to you and that it serves to improve the safety features in your process. Good Luck.